Active

When Active, a particular payment term will be available for use within the system.  De-activating a payment term that is currently associated with a project's invoice definition will have no effect on that project's setup (that is, that payment term will continue to be used for that project).   De-activating a payment terms indicates that it can no longer be associated when defining any new project billing invoice settings (nor available when updating an existing project's billing setup).

Essentially, de-activating a payment term prevents it from being associated with anything that it is not already associated with.